1. Field of the Invention
The invention relates to a photoactivatable coating composition comprising at least one photoinitiator and a base-catalysed polymerisable or curable organic material comprising at least one polyisocyanate and at least one compound comprising isocyanate reactive groups, and to its use for the preparation of coatings with a rapidly processable surface at ambient temperature.
2. Discussion of the Prior Art
Photoactivatable coating compositions of the type indicated above are known from, int. al., U.S. Pat. No. 4,369,206. In this document use is made of ammonium salts of α-ketocarboxylic acids as photoinitiator, and the photoactivatable coating compositions comprise polyurethane or epoxide resin precursors hardening in the presence of amines. A drawback to the known compositions is that they are only cured in places which are readily accessible to UV light. In the case of three-dimensional surfaces, or where the presence of pigments does not allow the UV radiation to penetrate into lower layers, the curing speed is too low.
EP-A-0 898 202 discloses the photogeneration of amines from α-amino acetophenones as latent base catalyst in a base-catalysed coating composition. The curable systems only comprise organic compounds which are capable of reacting in a base-catalysed reaction or a condensation reaction. Specific mention. is made of a (poly)alcohol and a (poly)isocyanate. In order to increase the curing speed in places which are not readily accessible to UV light, mention is made of the possible use of an additional unblocked base catalyst, which, however, requires the use of an additional thermal step.
The invention now provides coating compositions which can be cured by UV radiation and have an acceptable curing speed at ambient temperature in places which are not readily accessible to UV light, which compositions comprise at least one photoinitiator and a base-catalysed polymerisable or curable organic material comprising at least one polyisocyanate and at least one compound comprising isocyanate reactive groups.